Generally, a read in region is located at the innermost circumferential portion of a DVD (for example, of a DVD-RW), and in this region there is recorded a TOC (Table Of Contents), in which the running time period and the start position of each item are recorded. When replaying the DVD, in order to read out this TOC, a so-called “re-zero” or initialization operation is performed, in which the position of a pickup head (“PUH”) is set to (i.e. is determined as being) this read in region, which is at a position 24.3 mm˜25.8 mm from the inner circumferential edge of the DVD, and is stopped there.
However, more precisely, since sometimes there may be some deflection in the disk, the position to which the PUH is set and stopped in this re-zero operation is a predetermined position which is determined in the disk device in advance, “corresponding” to the read in region if, hypothetically, a disk were to be loaded in which the deflection is zero. In other words, the target position for performing the re-zero operation is determined as being, not by any means a position upon the disk, but rather with reference to a predetermined absolute position with respect to the disk device main body. In this specification it will be supposed that, when the technical terms “re-zero operation” and “position determination to within the read in region” are used, they are intended to convey this meaning.
A disk replay device which performs such position determination to within the read in region is disclosed in Japanese Laid-Open Patent Publication 2005-332525. In this patent document, the concept is described of, when a predetermined supply time period has elapsed during position determination of the PUH to the read region, supplying a re-zero braking pulse having a voltage value of 2 V˜3 V to the thread motor. According to this method, it is possible to positionally determine the PUH to within the read in region, which is the target, in an accurate manner, irrespective of any variation in the minimum start voltage of the thread motor.
And, in Japanese Laid-Open Patent Publication Heisei 5-217182, there is disclosed a recording medium drive device which positionally determines the PUH to a position which corresponds to the read in region. In this patent document, a structure is disclosed in which the thread motor is driven and, by the PUH contacting against a switch which is provided at the inner circumferential edge and decelerating when this switch is turned ON, the PUH contacts against an end stop portion and the PUH is stopped. It is stated that, according to this structure, it is possible to perform position determination to the read in region in an accurate manner.
However, with the device described in Japanese Laid-Open Patent Publication 2005-332525, since the re-zero braking pulse voltage is supplied when performing position determination to within the read in region, it is necessary to perform adjustment by experiment, in order not to shift the PUH in the opposite direction. Furthermore, with this device described in Japanese Laid-Open Patent Publication 2005-332525, even though consideration is given to variation of the minimum start voltage of the feed motor, there is no concept of evaluating what may be the extent of the state of variation of this minimum start voltage in each individual case, so that there has been the problem that it cannot cope with long term change and the like. As a result, for example, the user has been subjected to various causes of apprehension, such as for example that, no matter how many times the re-zero operation may be performed, after loading a DVD he will not be able to play it.
And, with the method described in Japanese Laid-Open Patent Publication Heisei 5-217182, when reading out the read in region, since each time the PUH or the like contacts against the stop plate and is positionally determined by being stopped, accordingly the PUH or the like experiences a shock load each time even though it is decelerated, so there has been a fear that it may easily undergo long term change or damage.
The present invention has been conceived in consideration of the problems described above, and its object is, in the re-zero operation of a disk device, to evaluate the ease of performing shifting of the PUH in each individual case, and to perform position determination to within the read in region in a more accurate manner based upon this evaluation. Furthermore, the present invention also takes as its object, if the re-zero operation has failed, to evaluate the ease of performing shifting of the PUH in each individual case, while performing a retry of the re-zero operation (hereinafter termed a “short re-zero operation”), and to perform position determination to within the read in region in a more accurate manner based upon this evaluation.